Process of roasting ores



E. B. KIRBY. v PROCESS OF ROASTING ORES, FURNACE PRODUCTS, ORE MIXTURES, AND THE LIKE.

APPLlCATlON HLED JULY 21. l9l4.

2 SHEETS-SHEET l.

1,3 1 6,726. Patented Sept. 23, 1919;

E. B. KIRBY. .PROCESS OF ROASTING ones, FURNACE PRODUCTS, ORE MIXTURES, AND THE LIKE. APPLICATION FILED JULY 2|. I914.

1,316,726. PatentedSept. 23,1919.

2 SHEETSSHEET 2- Mm M /j 5L @175 S UNITED STATES PATEN Ffio EDMUND B. KIRBY, OF ST. LOUIS, MISSOURI.

PROCESS OF ROASTING ORES, FURNACE PRODUCTS, ORE MIXTURES, AND THE LIKE Specification of Letters Patent.

Patented Sept. 23, 1919.

Application filed July 21, 1914. Serial No. 852,204.

and useful Improvement in Processes of Roasting Ores, Furnace Products, Ore Mixtures, and the Like, of which the following is a full, clear, and exact description.

This invention is a process or method of procedure by which one may quickly and definitely establish, control and regulate at all stages of a roasting operation the temperature of the individual grains of a mass of material under treatment, and the chemical composition of the gases in direct contact with said individual grains, to the end that desired results may be economically and quickly produced, regardless of the chemical composition of the material or its changes in chemical composition as the roast progresses.

In order to impart a clear understanding of the distinctions between the process hereinafter described and claimed and the processes heretofore used a brief'review of the prior art is deemed advisable.

In the ordinary ore roasting as distinguished from sinter roasting, one much used class of apparatus is such that constantly and irregularly varying gases of fuel combustion mingled irregularly with air admitted at various places is made to sweep rapidly over the surface of the crushed ore which constitutes a horizontal layer several inches thick upon the hearth of a suitable furnace receptacle. This poorly mixed current of gas escapes up the chimney with only a portion of its heat, and only a portion of its chemical efliciency utilized, since 7 there has neither been opportunity for effective contact with the grains of the material, nor time for the gases to react fully with them. Each grain beneath the surface of the layer is enveloped in a small volume of stagnant gases inclosed in the interstices of the material and composed of chance proportions of the overhead current and various products of the decomposition of the material itself. Not only are there very wide differences in the composition of the uncontrolled gas mixtures which are in actual contact with the individual grains but there are also wide differences in the temderatures of the grains themselves due to tie irregular conduction of heat from various parts of the furnace, irregularities of radiation of the flame from the furnace roof and sides upon the surface grains, heat differences in different parts of the furnace, etc. Moreover, any changes in either the temperature or chemical composition of the overhead current reach the underlying gralins of the mass very slowly and irreguar y.

Attempts have been made by stirring or lifting and dropping or moving the material about in the furnace to give each grain a turn-about exposure to all of these different conditions,trying in an indefinite and approximate wa to keep the worst of them within limits. %V'hile these expedients have unquestionably increased the efficiency of the process, nevertheless each grain obviously has a large percentage of lost time, including every period in itsindividual experience when it lay excluded from the roasting conditions which it should have had at that stage, and was not therefore progressing. It has also had to take its turn at all the present. 7

In mufile roasting, where gases of fuel consumption do not come in contact with the ore, but transmit their heat by conduction through the door underneath the ore and by radiation from the roof overhanging it temperature changes are produced more slowly and with even great difficulty. The air supply admitted to the muffle has been more or less Well regulated, but this only affects the conditions to which the mass as a whole is subjected, and does not control the conditions to which the individual grains are subjected.

In those processes of roasting where the ore generates its own heat, the general mass conditions are fixed by the air admitted to different portions of the charge, but the operation is subject to the same difficulties above mentioned.

In sinter roasting by the process now most commonly practised, a horizontal layer of ore mixture, which has'been compounded to have the required chemical composition (if the native ore didnot have that composition) is first gnited by direct contact with a flame or with burning fuel; and a current of air is thereafter drawn or blown through it to support the combustion. Generally speaking, this entire la er is progressively subjected to the same Xed and unchangesubjected. Ore roasting as heretofore prac tised has not heretofore been nearly as efficient or economical as it should be in any case. Additionally it has been known that ore roasting to be most eflicient and most satisfactory required many refinements in the treatment of the ores, such as confining sulfatization within certain desired limits, avoiding the formation of certain insoluble ferrites, and also the sintering of ore mixtures containing other than certain proportions of sulfur, etc., these refinements having been either too expensive to practice or wholly impossible.

1 In the process herein described and claimed a charge of the material com-' minuted to the required fineness is confined in a receptacle wherein it is substantially isolated from any externally generated heat or gas, save those of the current to be described, and a current of prepared gases having certain definite composition known to be required at the time with the particular ore under treatment to produce best results, is preheated to the definite temperature required but is never heated to such temperature as that in view ofthe other conditions the ore will be caused to or allowed to ignite or break into confiagration; and this gas so preheated to the required temperature, and having the required chemical composition is caused to flow through the interstices of the comminuted ore and in intimate contact with the individual grains thereof until desired results are attained; and to whatever extent may be necessary or desirable the chemical composition of the gas, and its temperature may be definitely varied at different stages of the roasting operation.

Of course, to carry out said process in any practical way, some apparatus is required, and such an apparatus, and various modifications thereof are fully described in a copending application.

In the drawing Figure 1 is a 'plan view somewhat diagrammatic in character of an apparatus suitable for the practice of this process. Fig. 2 is a longitudinal vertical section through one-end of the furnace sh0wing the means by which the comminuted material is suitably confined and the means by which the preheated and properly com- .fan alone might be pounded gas current is delivered into and withdrawn from the comminuted ore.

The apparatus comprises a number of appliances operatively connected. It is shown in Fig. 1 in a complete form adapted for use with all kinds of ores and for the problower 2 for forcing the prepared gases into.

said receptacle;'a hot blast stove 3 for preheating the prepared gas, a vacuum fan or blower 4 for withdrawing the gas from said receptacle, an incoming gas main 7, the outgoing gas main 8, a separating device 5 for collecting the dust and fume in the outgoing gas current; the chimney 6 into which said outgoing main discharges, and suitable pipes, valves, etc., as hereinafter described.

All parts of this apparatus, except the furnace 1 and the component parts thereof to be described, consists of standard or well known appliances, each of which is constructed in a great variety of designs. I do not limit myself to any particular form or mentioned appliances are not required; for

example, itis self evident that with some ores either the pressure fan or the vacuum made to move the current.

The hot :blast stove 3 is of the pipe class,- that is to say, the stove includes a combustion chamber 3 connected with a chimney 13, an oven 3", and suitable pipe coils 10 in the oven. These pipe coils are connected in series with the gas supply pipe '11 which leads away from the blast fan 2, and with the incoming gas main 7 The various coils are connected with a by-pass pipe 12 which connects pipe 11 with the gas main 7. In

the piping are valves 11 12, 3, 3 3 by the manipulation of which the blast current draws such gases as are necessary for producing the particular gas mixture required. The pipe 15 is that through which air may be drawn, and it contains a gaged valve 15 by which to regulate the size of the orifice through which the air must flow, and thereby to regulate the rate of flow. 1-6 represents a pipe (and there may be any number of pipes of this sort) connected with the inlet pipe 14, and is to be connected with a source of the particular kind of gas which may be required in the gas mixture, and each of these pipes will contain a gaged valve 16 by which to regulate the rate of flow of said gas from said container into pipe 14:. 17 represents a pipewhich con-, nects pipe '14 with pipe 18 through which the hot exhaust gases from furnace 1 are led to and discharged into chimney 6. The gaged valves 1"! and 18 provide means by which to determine what part of the said hot exhaust gases are allowed to go into the chimney, and what shall be allowed to go into inlet pipe 14. 19 represents a pipe for connecting the inlet pipe 14 with the combustion chamber 3 of the hot blast stove, and it contains a gaged regulating valve 19.

As many of these gas supply pipes with regulating valves may be-provided as may be required, and they may be connected with suitable sources of the desired gases. -With the construction shown, however, provision is made for preparing, as required for use and immediate delivery to the fan, a gas mixture made up'of measured and therefore properly proportioned partsof air, the hot gaseous products of fuel combustion" from the stove combustion chamber containing C0,, the hot exhaust gases discharged from the ore .roasting furnace, and any other needed gas; and for most ore roasting operations, desired results can be obtained by mixtures made up of suitable proportions of these gases, provided that, as they pass from the fan to the inlet main 7 they are preheated to the required temperature. V

The furnace is preferably a rectangular receptacle without a top. In it aretwo ser1es of gas conduits which, when said chamber is filled with comminuted material, will be buried therein. One group of these conduits will be connected with the inlet main 7, and will hereinafter be referred to as incoming gas conduits, while the other group of conduits will be connected with the exhaust main 7 and will be hereinafter referred to as outgoing gas conduits. The

conduits of one grou must be arranged in such juxtaposition to those of the other group that the incoming gas passing through suitable properly distributed gas passages in the incoming gas conduits will flow through the interstices of the surrounding mass of material in the furnace receptacle, and thence into the outgoing gas conduits. Various forms of gas conduits may be employed, and the openings or passages for the discharge reception of gas may be of various for I As-shown in Fi 2, however, .each of the incom ng gas con nits 25, and each of the outgoing gas conduits 8'5 is a substantially ness of each vertical ore sheet, that is to say,

the distance between adjacent partition conduits must be such that the current of gas can flow across this space through the interstices of said sheets of comminuted ore.

For a more complete description of an apparatus and the various modifications of an apparatus suitable for the practice of this process with various specific kinds of ore, reference may be had to the companion application hereinbefore referred to. It is perhaps sufiicient for the present to say that these partition conduits may be made of any material which is best adapted to the nature of the gas employed and the temperatures to which they are subjected. These partition conduits may have a large number of gas passages 33 made through their opposed walls, and these gas passages may have any particular form and be of any particular size best adapted to the particular ore to be treated. The upper and lower parts of these partition walls should be imperforate. In charging the furnace, inert material, such as ore which has already been roasted, should be packed between the imperforate lower part of these partition conduits in sufiicient quantity to serve as a seal, preventing, the downward escape of gas. Next above this inert material and between the perforated walls of the partitions will be packed the unroasted comminuted ore or other material to be treated. Above this and between the imperforate upper parts of the partitions will be packed a suflicient quantity of material which may be unroasted ore, to act as a seal to prevent the escape upward of said gas. During the roasting operation the ore sheets in the several ore cells between partitions will be held by suitable gates 57 at the lower ends of said ore cells.

Before roasting any ore or other material according to the herein described process and with the above described apparatus or any other suitable apparatus, one should first determine what combination of gases will produce in the most satisfactory degree the desired results upon that particular ore. and at what temperature these results will be produced in the more satisfactory degree, and whether, as the composition of the ore under treatment is varied by the treatment, it is desirable to change either the components of the gas current or its temperature, and to what extent and how.

These things being definitely determined, the ore or other material, comminuted to the proper degree, is charged into a receptacle in a comparatively thin layer, care being taken to isolate the charge therein from any externally generated heat, save the flameless heat which is delivered thereto by the preheated gas current. Then the compounded gas containing definite proportions of the required component gases, and preheated to the determined temperature, is caused to flow swiftly through the interstices of the charge and in intimate contact with the grains thereof, thereby producing, uniformly and quickly, those results upon said charge which said gas, so preheated, is adapted to produce, and some of the gas after passing through the charge may be recirculated through it in order to obtain itsfull effect; this recirculation being carried to any extent that is found desirable.

The definite composition of the gas current and the definite temperature to which it is preheated are under perfect control independently of each other and are regulated by being immediately varied as required during the progress of the roasting operation. Any adjustment of temperature made by the stove by-pass valves or of composition made by the gas sup-ply valves, is felt within a few seconds and with substantial uniformity by every individual grain of the charge.

Both the temperature of the current and the percentages of its active components are regulated to the definite points required within whatever limits of accuracy may be necessary. The temperature regulation is guided by suitable pyrometers placed in the gas current and also in the charge of material. The regulation of composition is guided by any suitable devices of the class known in the arts for indicating or determining either continually or at intervals the percentage of any gaseous component to be governed.

As one illustration of the many new results which may be accomplished by this definite andv perfect regulation, there are ores, for example. which, when the roasting operation is concluded, should be delivered in a sintered instead of a comminuted condition, but which contain an excess percentage of oxidizable components over that required for sintering. In the treatment of such ores the percentage of free oxygen in the gas current should be kept low so that this excess of oxidizable components will be slowly oxidized. If it Were not, the great heat developed internally by the rapid oxidation of these components might produce undesirable changes in the ore. The percentage of free oxygen in the gas current may be kept low by diluting the air, to whatever extent may be necessary, by including in the gas mixture air with more or less of the hot exhaust gas which has passed through the ore, or w1th more or less of the gaseous products of combustion from the stove combusincreasing the percentage of free oxygen in the gas current, and this sintering may be assisted by also increasing the pressure of said gas as it flows through the interstices of the charge.

I believe that no method of ore roasting has heretofore been suggested by which one could subject all of the individual grains of the material to be treated at substantially the same time to substantially uniform conditions, or could make those conditions precisely such as were most efficient for the time being with any kind of ore or could almost immediately definitely alter and regulate those uniform distributed conditions as required for the production of desired results in the highest degree.

In cases Where the ore becomes sintered or agglomerated in roasting and the resulting sheet of sintered ore tends to adhere to the walls of the furnace or to the side of the outgoing conduit or to choke its apertures, such adhesions or choking may be prevented by so charging as to deposit a thin layer of non-adhering material along the face of the ore sheet which is in immediate aontact with said walls or said outgoing conuit.

Such non-adhering material may, for instance, be the finesreturned from the roasted product or fluxes which are to be used with it afterward, or on the other hand it may be the more infusible components or the coarser lumps of the charge itself separated from it temporarily for this purpose.

Having described my invention, I claim:

1. The process of roasting ores, furnace products, ore mixtures and the like which consists in confining the material in a suitable comminuted condition in a thin sheet in a receptacle; in causing the passage through the interstices of said material and in intimate contact with the individual grains thereof of a compounded gas made up of definite proportions of the gaseous components required, which compounded gas 1s preheated to the definite temperature required before it is discharged into said material, in restricting the percentage of oxygen in said mixture for a time to such a degree that sintering of the material will not take place; and in, at the proper time, suddenly increasing the'percentage of oxygen in the gaseous compound to a degree such as will induce sintering.

2. The process of roasting ores, furnace products, ore mixtures and the like which consists in placing the charge in a receptacle where it is substantially isolated from anyheat or gases save those of the current to be described; and in causing a prepared current. of gases to flow-through the interstices of the charge and in intimate contact with the individual grain thereof and in pre heating said current to the definite temperature required before it comes in contact with the charge and in having said current include for recirculation a greater or less proportion of the outflowing current from the charge.

In testimony whereof, I hereunto afiix my signature in the presence of two Witnesses.

EDMUND B. KIRBY.,

Witnesses:

E. L. THURsToN, L. I. PORTER. 

